Typically, afterburners and thrust augmentors in turbojet or turbofan engines have one or more fuel spray devices which comprise a fuel spray manifold of elliptical cross-section extending circumferentially therein and a series of fuel pintles spaced around the manifold circumference. Each pintle includes a threaded attachment end received in a threaded aperture in the manifold and a conical metering tip operatively associated with an ejection orifice in the manifold. Upon application of fuel pressure inside the manifold, the elliptical manifold will distend to a more circular cross-section, causing the ejection orifice wall to move axially away from the conical pintle seat to allow fuel to discharge in controlled manner. Such fuel spray devices are shown in U.S. Pat. No. 3,871,063 issued Mar. 18, 1975 to Robert M. Halvorsen.
It has been the practice to insulate the fuel spray manifold of such devices by placing a similarly shaped heat shield at least partially therearound to provide a dead air space therebetween. For example, such a shielding technique has been used in the thrust augmentor of the F-100 gas turbine engine manufactured by Pratt & Whitney Aircraft to provide protection against the hot gases flowing from the turbine section.
Recently it has been proposed to use such fuel spray devices without heat shielding. However, as a result of the considerable heating of the fuel in the manifold by the hot turbine gases, prior art workers have expressed concern about fuel vaporization problems inside the manifold and possible shut-off of fuel flow as a result. Prior art workers have called for a higher than normal fuel pressure in the fuel spray manifold to suppress anticipated fuel vaporization at lower than normal fuel flow rates.